The aim of this research is to delineate the sensory cues (internal and external stimuli) which control and organize species-typical behavior in the rat pup during its early development. A variety of observational studies using time-lapse video tape recordings will be applied to the description of pup development within a semi-natural nest environment and an analysis of changes in general social preferences and specific olfactory preferences during ontogeny. The role of infant high frequency vocalizations will be studied with respect to maternal behavior and the physiological states that induce "ultrasound" production during development. Nursing behavior will be studied as a behavior system that disappears with maturation. The factors that organize nursing activities and the changes in these controls during weaning will be studied with particular emphasis on olfactory control of the behavior. The parameters of the normal ontogeny of olfaction will be investigated specifically, employing natural, unconditioned responses to a variety of pure chemical and biological odors. The results will be compared to the development of normal behavior to clarify the relationship between sensory and behavioral maturation.